I've had 2 dedicated servers with 1and1 before
the first one i got was reliable and i had it running for a good 18 months without a single outage (only downtime was caused by me rebooting it setting something up or doing updates etc)
then i got a second for a different purpose, this one i needed plesk on it for a convenient control panel for customer access and this is where the problems began. the plesk image they used to install the servers was broken and installed a broken system that didn't work. I asked for the plesk keys so i could use the "clean system" image then install plesk myself and nothing, phoned them and "you must select plesk from the control panel, then it works" so i used the plesk image and phoned the "first level support" again "it's not working".. "it looks like it is working from my system" - of course after i had to talk him through how to log in to plesk (wtf was he looking at to claim it was working without error??) he finally admitted a problem, after several hours on the phone they finally agreed to a refund and cancellation. of course i did check the server logs to see where he had logged in to the server from (after I had had to tell him how to use plesk, great support!) and i'm sure you wouldn't be suprised at the fact that it was an ADSL connection in south america (i guess someone said indian call centers were a bad idea, so they went for somewhere just as bad that wasn't called india?)
that's when i moved the other server away from them as well!
shared hosting accounts you can't rely on, there will always be problems with reliability with other customers etc unless you are paying extremely highly for it, in fact i'd say i doubt you can find a low cost shared host that can handle a busy website (even just a few hundred thousand users a day busy) that uses mysql (servage seem good for static files unlike many, however their mysql is just as bad as the others)
for dedicated hosting 1and1 were very reliable and have a decent network, however the problem is their support, or should i say the problem is there isn't support.
of course if you do have serious reliability requirements then the best solution is geographically diverse servers with different providers, 2 cheap "budget" dedicated servers with everything mirrored and load balanced between them would give better reliability than a typical "high availability" host, but cost not much more than budget hosting (of course for small sites it's likely budget hosting can be much cheaper, but then that sort of site wouldn't have the same reliability requirements)
I currently run one site with high availability requirements (relatively low traffic, around 100,000 hits/day) from a pair of really cheap VPS accounts (£5/month and £6/month), i get the prices of budget hosting but i've yet to have an outage! (the only problem with such a setup is synchronizing dynamic content, which often means custom made scripts, not a problem for me as it's all custom made anyway but some people like to just click the "install an ecommerce site" button)